static void Main(string[] args)
    {
      DateTime now = DateTime.Now;
      string time = now.ToString("yyyy-mm-dd hh:mm:ss"); 
      Console.WriteLine(time);
      Console.ReadKey();
    }

public static string DateToString(DateTime dt)
    {
      return dt.ToString("yyyy-mm-dd hh:mm:ss");
    }

static void Main(string[] args)
    {
      DateTime now = DateTime.Now;
      string time = DateHelper.DateToString(now);
      Console.WriteLine(time);
      Console.ReadKey();
    }

public static string DateToString(this DateTime dt)
    {
      return dt.ToString("yyyy-mm-dd hh:mm:ss");
    }

static void Main(string[] args)
    {
      DateTime now = DateTime.Now; 
      string time = now.DateToString();
      Console.WriteLine(time);
      Console.ReadKey();
    }

public static int StrToInt(string s)
{
  int id;
  int.TryParse(s, out id);//这里当转换失败时返回的id为0
  return id;
}

string s = "abc";
int i = StrToInt(s);

string s = "abc";
int i = s.ToInt();

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
 
namespace W.Common
{
  public static class EString
  {
    /// <summary>
    /// 将字符串转换为Int
    /// </summary>
    /// <param name="t"></param>
    /// <returns>当转换失败时返回0</returns>
    public static int ToInt(this string t)
    {
      int id;
      int.TryParse(t, out id);//这里当转换失败时返回的id为0
      return id;
    }
  }
}

/// <summary>
  /// 此时间是否在此范围内 -1:小于开始时间 0:在开始与结束时间范围内 1:已超出结束时间
  /// </summary>
  /// <param name="t"></param>
  /// <param name="startTime"></param>
  /// <param name="endTime"></param>
  /// <returns></returns>
  public static int IsRange(this DateTime t, DateTime startTime, DateTime endTime)
  {
    if (((startTime - t).TotalSeconds > 0))
    {
      return -1;
    }
 
    if (((endTime - t).TotalSeconds < 0))
    {
      return 1;
    }
 
    return 0;
  }

using System;
using System.Collections.Generic;
using System.Linq;
using System.Web;
using System.Web.UI;
using System.Web.UI.WebControls;
using W.Common;//这里引用扩展方法所在的命名空间
 
namespace webtest
{
  public partial class _Default : System.Web.UI.Page
  {
    protected void Page_Load(object sender, EventArgs e)
    {
      use1();
      Response.Write("<br />");
      use2();
    }
 
    /// <summary>
    /// 没有用扩展方法
    /// </summary>
    private void use1()
    {
      string s = "abc";
      int i = StrToInt(s);
      Response.Write("没有用扩展方法:" + i);
    }
 
    /// <summary>
    /// 使用扩展方法
    /// </summary>
    private void use2()
    {
      string s = "2012";
      int i = s.ToInt();
      Response.Write("使用扩展方法:" + i);
    }
 
    public static int StrToInt(string s)
    {
      int id;
      int.TryParse(s, out id);//这里当转换失败时返回的id为0
      return id;
    }
  }
}